add EmacsRequirement

Closes Homebrew/homebrew#39326.

Signed-off-by: Xu Cheng <xucheng@me.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/Library/Homebrew/requirements/emacs_requirement.rb b/Library/Homebrew/requirements/emacs_requirement.rb
new file mode 100644
index 000000000..1da3ecd04
--- /dev/null
+++ b/Library/Homebrew/requirements/emacs_requirement.rb
@@ -0,0 +1,30 @@
+class EmacsRequirement < Requirement
+  fatal true
+  default_formula "emacs"
+
+  def initialize(tags)
+    @version = tags.shift if /\d+\.*\d*/ === tags.first
+    raise "Specify a version for EmacsRequirement" unless @version
+    super
+  end
+
+  satisfy :build_env => false do
+    next unless which "emacs"
+    emacs_version = Utils.popen_read("emacs", "--batch", "--eval", "(princ emacs-version)")
+    Version.new(emacs_version) >= Version.new(@version)
+  end
+
+  env do
+    ENV.prepend_path "PATH", which("emacs").dirname
+  end
+
+  def message
+    s = "Emacs #{@version} or later is required."
+    s += super
+    s
+  end
+
+  def inspect
+    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
+  end
+end